I can confirm this bug is present in 6.5.2. The issue was due to the JSON blob being parsed with the default "render" option, which prepares it for rendering in markup. This would only be present in attributes passed using a JSON payload with the Remote API Call action. The fix will be included in the upcoming release, or you can view the diff here: https://github.com/X...5e25604d87040a2. Thank you for reporting this issue!